Technical Field
The disclosed technology relates to transmission lines for high performance radio frequency applications.
Description of the Related Technology
Transmission lines can be implemented in a variety of contexts, such as on a packaging substrate or printed circuit board (PCB). Multi-layer laminate PCBs or package substrates are extensively used in radio frequency (RF) applications.
RF circuits, such as power amplifiers, low noise amplifiers (LNAs), mixers, voltage controlled oscillators (VCOs), filters, switches and whole transceivers have been implemented using semiconductor technologies. However, in RF modules (for example, an RF front-end module including power amplifiers, switches, and/or filters), single chip integration may not be practical due to different blocks being implemented in different semiconductor technologies. For instance, a power amplifier may be formed by a GaAs process, while related control and/or bias circuitry may be formed by a CMOS process.
Long transmission lines and/or other on-chip passives can consume large chip area. Consequently, multi-chip module (MCM) and/or system in package (SiP) assembly technology can be used to achieve low cost, small size and/or high performance in RF modules. Laminate technology can be used for MCM assembly, in which transmission lines are implemented on a laminate substrate. Conductor loss in such transmission lines can have a significant impact on the performance of any of the elements in the MCM. Accordingly, laminate plating technology can impact RF performance significantly.
The cost of laminate technology can be driven by the choice materials for performance and/or assembly needs. RF SiPs that use gold (Au) wire bonding to connect RF circuit elements to transmission lines can use a variety of different finish platings such as lower loss, more expensive NiAu (for example, due to thicker Au) or higher loss, less expensive NiPdAu. Accordingly, a need exists for cost effective, high performance technology for RF transmission lines.